The 55th Division was an infantry division of the British Army's Territorial Force (TF) that saw extensive combat during the First World War. It was raised initially in 1908 as the West Lancashire Division. Following the outbreak of the First World War, in 1914, the majority of the division's men volunteered for overseas service. Those who did not volunteer were used to form new reserve units, and on 31 August 1914 these were used to create the 2nd West Lancashire Division. Rather than being deployed as a whole formation, the West Lancashire Division was broken up during 1914 and 1915, as its troops were dispatched piecemeal to the Western Front. As each left, they were replaced by reserves. When the last volunteers departed for overseas service, the remnant of the division was amalgamated with the 2nd West Lancashire Division, and the West Lancashire Division ceased to exist.

The Battle of the Lys, also known as the Fourth Battle of Ypres, was fought from 7 to 29 April 1918 and was part of the German spring offensive in Flanders during the First World War. It was originally planned by General Erich Ludendorff as Operation George but was reduced to Operation Georgette, with the objective of capturing Ypres, forcing the British forces back to the Channel ports and out of the war. In planning, execution and effects, Georgette was similar to Operation Michael, earlier in the Spring Offensive.